1. Field of the Invention
The present invention relates to a transmission/reception apparatus and modulation system estimation method, and more particularly, to a transmission/reception apparatus adaptively varying a modulation system and modulation system estimation method therein in a mobile communication with a plurality of carrier waves.
2. Description of the Related Art
Conventional transmission/reception apparatuses adaptively varying a modulation system are, for example, disclosed in Japanese Unexamined Patent Publications HEI9-186635 and HEI10-247955.
The general description of the conventional transmission/reception apparatuses is explained below using FIG. 1. FIG. 1 is a partial block diagram illustrating a schematic configuration of a conventional transmission/reception apparatus. Herein it is assumed that two types of modulation systems are switched to be used, and the switching of the modulation systems is performed based on channel quality information estimated from a received signal.
In FIG. 1, selector 11 switches transmission data and information to notify a communication partner station of a modulation system that this apparatus uses (hereinafter referred to as modulation system information) to selectively output to modulator 12.
Modulator 12 determines the modulation system based on a channel quality of a received signal estimated in channel quality estimator 18 described later, and according to the modulation system, modulates the transmission data and modulation system information. Namely, as the channel quality becomes more excellent, it is possible to use a multivalue modulation with the larger number of bits per symbol to perform the modulation.
IFFT processor 13 performs inverse fast Fourier transform (IFFT) processing on the modulated transmission data and modulated modulation system information. Transmission processor 14 performs transmission processing on the IFFT processed transmission data and IFFT processed modulation system information to output a transmission signal.
Reception processor 15 performs reception processing on a received signal. FFT processor 16 performs fast Fourier transform processing on the reception processed received signal. Demodulator 17 demodulates the FFT processed received signal.
Channel quality estimator 18 estimates a channel quality from the demodulated received signal. Selector 19 separates the demodulated received signal into data and modulation system information, and outputs the data to first decider 20 and second decider 21, and further outputs the modulation system information to selector 22.
First decider 20 makes a decision on a received symbol according to the first modulation system on the assumption that the received signal is modulated with the first modulation system. Second decider 21 makes a decision on the received symbol according to the second modulation system on the assumption that the received signal is modulated with the second modulation system. Selector 22 selects either of an output from first decider 20 or second decider 21 based on the modulation system information to output as a demodulated signal.
Thus, the conventional transmission/reception apparatus adaptively varying the modulation system transmits the modulation system information along with the transmission data to the communication partner station. Therefore, since the reception station can recognize the modulation system to be used to make the decision, the station can obtain accurate demodulated signals when the modulation system applied at the time of transmission is adaptively varied.
In the conventional transmission/reception apparatus, however, since it is necessary to transmit the modulation system information besides the transmission data, the transmission efficiency deteriorates.